Distributed Bragg Reflectors (DBRs) are a fundamental component of optical devices requiring an optical gain, such as various types of semiconductor lasers. Conventional vertical DBR's are formed from lattice-matched alternating semiconductor layered materials. These materials provide a small difference in index of refraction between adjacent layers. As a result, a high number of pairs are required in a conventionally formed DBR to obtain desired reflectivities, e.g., about 25 to 40 pairs to attain reflectivities as high as 99.9%, depending on the difference of the index of refraction in adjacent layers.
Lateral wet oxidation has been used to form a DBR in single crystal semiconductor materials. Al-bearing semiconductors are oxidized, and the technique has produced DBRs in, for example, vertical-cavity surface-emitting lasers. Operation of these types of devices was possible in certain wavelength ranges. Long wavelength devices were not realized due to a lack of high quality oxide layer in the laterally oxidized semiconductor devices. In addition, portions of the visible spectrum were not supported by the DBR's formed by oxidation due to absorption of light. These types of DBRs are also limited to lattice matched substrates, limiting their application.
Thus, there is a need for an improved DBR and a method for forming DBRs which addresses the aforementioned drawbacks. The method of the invention is directed to this need.